Recently, in addition to an automotive vehicle discharge emission regulation, it is required to regulate an evaporative fuel emission. For example, the California Air Resources Board (i.e., CARB) as well as the U.S. Environmental Protection Agency (i.e., EPA) require detection of evaporative emission leakage from a small opening of a fuel tank of an automotive vehicle.
In view of detecting an evaporative emission leakage, U.S. Pat. No. 5,146,902 (JP-A-5-272417) and U.S. Pat. No. 5,890,474 (JP-A-10-90107) disclose evaporative emission leak detection systems for detecting leakage of fuel vapor leaking outside a fuel tank. These prior arts utilize a pressure difference between an inside and outside of the fuel tank. The pressure difference is provided by increasing or decreasing the pressure of the fuel tank with a pump. When leakage exists, a pumping load of the pump changes in accordance with size of leakage opening. Therefore, the evaporative emission leakage can be estimated by measuring the pumping load change.
However, when the pump increases the pressure of the fuel tank, i.e., the pump pressurizes the fuel tank, the fuel vapor is released outside the fuel tank at every detection time. Further, when the pump decreases the pressure of the fuel tank, i.e., the pump depressurizes the fuel tank, the fuel vapor may be eliminated by a canister. However, the residual fuel vapor, which is not eliminated by the canister, penetrates into the pump. When the pump is driven by a brush motor, the residual fuel vapor adheres to a sliding portion of the pump, for example, a sliding portion of a brush. Therefore, the sliding portion will be abraded. Moreover, abraded powder of the sliding portion adheres to a commutator of the motor, so that the commutator will be abnormally abraded. Thus, the motor operation becomes unstable and a life time of the motor decreases. Further, operation characteristics of the motor deteriorate with age because of an abrasion of the brush and the commutator, so that the leak detection system does not detect leakage accurately.